Acetylcholine muscarinic receptors have been thoroughly studied for some time and it is now commonly acknowledged that the M3 receptor is responsible of the contractile effect of acetylcholine in the smooth muscle of intestinal tract, urinary bladder and bronchi. M3 antagonist are currently used in therapy to induce bronchodilation and inhibit gastrointestinal motility and urinary bladder contraction. However, in the above-mentioned tissues, M2 receptors are also present; since M2 receptors are a major population in the smooth cardiac muscle, in order to avoid side-effects on the cardiac muscle the research has focused on the finding of selective M3 antagonists.
Recently it has been reported that tiotropium, the first drug in a new generation of antimuscarinic drugs, possesses unique properties of “kinetic selectivity” with fast dissociation from M2 receptors and very slow dissociation from M1 and M3 receptors.
Therefore both good selectivity for, and slow dissociation from the M3 receptors are deemed important for new antimuscarinic drugs efficacious by inhalation in a once a day administration for the treatment of respiratory diseases and in particular inflammatory or obstructive airway diseases such as asthma and chronic obstructive pulmonary disease (COPD).
Selective M3 antagonists containing the quinuclidine nucleus are, for instance, disclosed in WO 02/00652, WO 02/051841, WO 03/053966 and WO 2004/000840.
In particular, WO 02/00652 and WO 03/053966 relate to quinuclidyl-carbamate derivatives provided with affinity for the human M3 receptor and selectivity for the M3 receptors over the M2 receptors.
WO 02/051841 and WO 2004/000840 disclose antimuscarinic quinuclidine derivatives showing high affinity and selectivity for the muscarinic M3 receptors over the M2 receptors, that, according to the inventors, also show bronchodilator activity in the test on bronchospasm in guinea pig, with high potency and a long duration of action, but no data are reported.
Therefore, the muscarinic antagonists of the prior art are mainly characterised by their selectivity for the M3 receptors over the M2 receptors and even though in WO 02/051841 and WO 2004/000840 it is also said in generic terms that the compounds are provided with a bronchodilator activity and a long duration of action, no demonstration is given.